In recent years, with increased demand for gases at locations relatively remote from their source, it has been the practice to provide liquefaction plants at the source, a conveyance or vehicle capable of transporting the liquefied gas over long distances, and a regasification plant proximal to the ultimate consumer at which the liquefied gas is converted into the gaseous state for use.
Such systems are especially important in the present power crises since natural gas (i.e. methane) may be readily available in regions quite remote from industrial sites, but may be in relatively short supply in industrial and residential areas. Hence the transportation of liquefied natural gas over long distances in an economical and safe manner is of the utmost importance.
Various transportation conveyances have been proposed for the purpose indicated and by far the most feasible is the ocean-going tank ship. There have already been described in the literature and constructed assemblies of receptacles, having a length which is considerable relative to their diameters, for disposition in the thermally insulated cargo compartments of such vessels. Thus a multiplicity of such individual receptacles may be disposed between decks or between the bottom of the hold and an overlying deck of a tank ship, the upper and lower ends of the individual receptacles being each secured to the deck and underlying floor with intervening layers of load-supporting thermal insulation.
The kinetic and inertial forces which are applied to the anchorages by the cargo upon rolling and pitching of the ship, however, have required that the tanks or receptacles be disposed in large measure above deck or that the decks be strengthened by massive reinforcements. To structurally stabilize the ship, therefore, a large part of the nominal cargo-carrying capacity may have to be sacrificed for structural stability and the ship may be invested with considerable deadweight. Furthermore, the cost of constructing such a vessel under existing principles of liquefied-gas storage may be inordinately high, especially in view of the low useful capacity of the ship. The economy of liquefied-gas transport in these vessels is generally low.